Is there an event / callback that is accessible from the JS client to know when certain events like publish timeout happens?
Yes, there is an event/callback message on WebSocket object. You can use callbackError section like in this link: https://github.com/ant-media/StreamApp/blob/master/src/main/webapp/index.html#L735
You can check this guide for all WebSocket messages: https://github.com/ant-media/Ant-Media-Server/wiki/WebRTC-WebSocket-Messaging-Reference#websocket-error-callbacks